The present invention relates to a bar feeder with pre-feed device for an automatic lathe.
Feeders of the above type are already known. They comprise an elongated box-like body constituted by a lower tray and by a cover which can be lifted with respect to the lower tray. The tray and the cover respectively comprise mutually opposite slots which have a semicircular cross-section and which, when the cover is in the closed position, form a guiding channel in which a bar is deposited each time, said bar being pushed longitudinally by means of a bar pusher, in order to be inserted through a tubular spindle of a machine tool where the bar is machined section by section.
The bar pusher is supported so that it can slide within the cover, and in order to allow said pusher, when the cover closes, to be arranged behind the bar, said bar, before the cover closes, is fed forward by a suitable extent by means of a pre-feed device provided with an auxiliary pusher.
Such a device is disclosed for example in Italian utility model No. 195,220.
In conventional feeders, the pre-feed device comprises a carriage which is rigidly coupled to the motorization system and the auxiliary pusher has the same diameter as the bar pusher, since during the machining of the bar it must follow the bar pusher inside the guiding channel.
For small bars, in the order of 1-2 mm, the guiding channel is rather small and accordingly the front surface of the auxiliary pusher is rather limited. This circumstance, together with the fact that the guiding channel is employed for several bar diameters and that thin bars are also highly flexible, makes it very difficult to keep the auxiliary pusher in abutment against the bar. The bar, by flexing, tends in fact to disengage from the auxiliary pusher and to wedge between said auxiliary pusher and the wall of the guiding channel.
From a conceptual standpoint, it would be possible to increase the ability to pick up and push the bar by increasing the diameter of the auxiliary pusher, but this would also require an increase in the diameter of the guiding channel inside which the auxiliary pusher, by being rigidly coupled to the bar pusher, must move; as a consequence this creates once again conditions which facilitate the play of the bar inside the channel.